I've noticed this with a lot of kids in our neighborhood that do the same thing to me. I usually just smile and nod, or say "uh-huh" occasionally... they seem happy enough with that
I really don't expect myself to relate too much to it, or to be too interested. I guess I figure I've experienced a LOT of what they choose to talk about, and it really doesn't matter to me anymore. Sometimes they get all cranky, because I'll just say something like, "oh it will heal." Sometimes I can easily join in on children type conversations-probably because I have the 2 kiddos to relate things to.
It comes along like, "I fell down and hurt myself really bad." "oh?" "yeah, it hurt a lot and was bleeding." "oh Zack did something like that once." Then we have something to talk about, lol. Either that or I get pretty childlike and giggle and say "ewwww" when they show me and all, and they think that's fun for some reason... sometimes I draw their attention to those types of things just to gross them out and they like that kind of stuff, too, lol. But I gotta be in a good mood for it to go smoothly.
I always just remind myself, as long as you pretend you are interested, the kiddos think that you are and are happy with whatever response they get usually.
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Sorry about the incredibly long post...
"I enjoyed the meetings, too. It was like having friends." -Luna Lovegood